Chicken thymocyte-specific antigen identified by monoclonal antibodies: ontogeny, tissue distribution and biochemical characterization

Energy metabolism in developing chicken lymphocytes is altered during the embryonic to posthatch transition

Adequate energy status in lymphocytes is vital for their development. The ability of developing chicken lymphocytes to acquire and metabolize energy substrates was determined during embryonic days (e) and neonatal days (d) of life when primary-energy substrate metabolism is altered at the whole-animal level. In 3 experiments, bursacytes and thymocytes were isolated on e17, e20, d1, d3, d7, or d14 to analyze markers associated with glucose, glutamine, and lipid metabolism. Bursacyte glucose transporter-3 (Glut-3) mRNA abundance increased from d1 to d14 and hexokinase-1 (HK-1) mRNA abundance was maximum on e20 (P<0.05). Thymocyte Glut-1, Glut-3, and HK-1 mRNA abundance increased from e17 to d14 (P<0.05). HK enzyme activity increased from e20 to d3 in bursacytes and d3 to d7 in thymocytes (P<0.05). Glucose uptake by bursacytes and thymocytes was greater on d14 compared to d1 and d7 (P<0.05). Bursacyte and thymocyte sodium coupled neutral amino acid transporter-2 and glutaminase (GA) mRNA abundance increased from e20 to d7 (P<0.05). GA enzyme activity increased from e20 to d7 in bursacytes (P<0.05) and did not change in thymocytes. Carnitine palmitoyl transferase enzyme activity did not change over time in either cell type. These studies suggest that developing B and T lymphocytes adapt their metabolism during the first 2 wk after hatch. Developing lymphocytes increase glucose metabolism with no change in fatty acid metabolism and bursacytes, but not thymocytes, increase glutamine metabolism. Understanding the factors that regulate lymphocyte development in neonatal chicks may help promote their adaptive immune responses to pathogens in early life.

Reversible disruption of thymic function by steroid treatment

The effect of steroid treatment on the thymic output of T cells was examined in an avian model. Recent thymic emigrants in chickens transiently express the chicken T cell Ag 1 thymocyte marker, and thymic function can be monitored indirectly by measuring the levels of TCR gene rearrangement excision circles in peripheral T cells. Both parameters were used to show that intensive steroid treatment induces thymic involution and a profound reduction in the supply of naive T cells to the periphery. Conversely, resident T cells in the peripheral lymphocyte pool were relatively spared. Thymopoiesis immediately recovered following cessation of steroid treatment, concurrent with restoration of the thymic output of newly formed T cells. Repopulation of the peripheral T cell pool recapitulated the ontogenetic pattern of gamma delta T cell replenishment before alpha beta T cell reseeding, thereby indicating the complete recovery of thymic function after a course of steroid treatment.

NK and T cells constitute two major, functionally distinct intestinal epithelial lymphocyte subsets in the chicken

Non-mammalian NK cells have not been characterized in detail; however, their analysis is essential for the understanding of the NK cell receptor phylogeny. As a first step towards defining chicken NK cells, several tissues were screened for the presence of NK cells, phenotypically defined as CD8(+) cells lacking T- or B-lineage specific markers. By this criteria, approximately 30% of CD8(+) intestinal intraepithelial lymphocytes (IEL), but <1% of splenocytes or peripheral blood lymphocytes were defined as NK cells. These CD8(+)CD3(-) IEL were used for the generation of the 28-4 mAb, immunoprecipitating a 35-kDa glycoprotein with a 28-kDa protein core. The CD3 and 28-4 mAb were used to separate IEL into CD3(+) IEL T cells and 28-4(+) cells, both co-expressing the CD8 antigen. During ontogeny, 28-4(+) cells were abundant in the IEL and in the embryonic spleen, where two subsets could be distinguished according to their CD8 and c-kit expression. Most importantly, 28-4(+) IEL lysed NK-sensitive targets, whereas intestinal T cells did not have any spontaneous cytolytic activity. These results define two major, phenotypically and functionally distinct IEL subpopulations, and imply an important role of NK cells in the mucosal immune system.

Biochemical analysis of the Xenopus laevis TCR/CD3 complex supports the "stepwise evolution" model

The TCR/CD3 complex of a cold-blooded vertebrate, the amphibian Xenopus laevis, was biochemically characterized with a cross-reactive polyclonal antiserum recognizing a conserved epitope in the cytoplasmic domain of CD3E. The specificity and utility of this reagent was validated by Western blot analysis and immunoprecipitation of the well-characterized chicken TCR/CD3 complex. Cross-reactivity with the X. laevis CD3E protein was demonstrated by specific staining of sorted CD8+ cells. Immunohistology on both tadpoles and adult tissues suggests this antiserum will be instrumental in the localization of Xenopus T cells and most likely NK cells. Double staining of tissue sections with an anti-CD8 monoclonal antibody confirmed that this staining is specific. The antiserum was also used for the biochemical analyses of X. laevis TCR/CD3 complex. The 75-kDa alphabeta TCR heterodimer could be separated into a 40-kDa acidic TCR alpha chain and a 35-kDa basic TCR beta chain. Two CD3 proteins, both comigrating at approximately 19 kDa, were associated with the TCR heterodimer. Removal of N-linked carbohydrates yielded CD3 proteins of 19 kDa and 16.5 kDa, most likely representing the CD3epsilon and CD3gamma/delta homologues, respectively. An additional band of 110 kDa represents a multimeric complex of the TCR heterodimer covalently linked to a CD3 dimer. These properties of the Xenopus TCR/CD3 complex substantiate a stepwise evolutionary model for the CD3 protein family.

ChT1, an Ig Superfamily Molecule Required for T Cell Differentiation

The thymus is colonized by circulating progenitor cells that differentiate into mature T cells under the influence of the thymic microenvironment. We report here the cloning and function of the avian thymocyte Ag ChT1, a member of the Ig superfamily with one V-like and one C2-like domain. ChT1-positive embryonic bone marrow cells coexpressing c-kit give rise to mature T cells upon intrathymic cell transfer. ChT1-specific Ab inhibits T cell differentiation in embryonic thymic organ cultures and in thymocyte precursor cocultures on stromal cells. Thus, we provide clear evidence that ChT1 is a novel Ag on early T cell progenitors that plays an important role in the early stages of T cell development.

CTX, a Xenopus thymocyte receptor, defines a molecular family conserved throughout vertebrates

CTX, a cortical thymocyte marker in Xenopus, is an immunoglobulin superfamily (Igsf) member comprising one variable and one constant C2-type Igsf domain, a transmembrane segment and a cytoplasmic tail. Although resembling that of the TCR and immunoglobulins, the variable domain is not encoded by somatic rearrangement of the gene but by splicing of two half-domain exons. The C2 domain, also encoded by two exons, has an extra pair of cysteines. The transmembrane segment is free of charged residues, and the cytoplasmic tail (70 amino acids) contains one tyrosine and many glutamic acid residues. ChT1, a chicken homologue of CTX, has the same structural and genetic features, and both molecules are expressed on the thymocyte surface. We cloned new mouse (CTM) and human (CTH) cDNA and genes which are highly homologous to CTX/ChT1 but not lymphocyte specific. Similarity with recently described human cell surface molecules, A33 antigen and CAR (coxsackie and adenovirus 5 receptor), and a number of expressed sequence tags leads us to propose that CTX defines a novel subset of the Igsf, conserved throughout vertebrates and extending beyond the immune system. Strong homologies within vertebrate sequences suggest that the V and C2 CTX domains are scions of a very ancient lineage.

Thymic function can be accurately monitored by the level of recent T cell emigrants in the circulation

Expression of the avian chT1 thymocyte antigen persists on a subpopulation of peripheral T cells enriched in the DNA deletion circles created by alphabeta and gammadelta TCR gene rearrangements. The chT1+ cells are evenly distributed among all of the peripheral T lymphocyte compartments. The levels of chT1+ T cells in the periphery gradually decline in parallel with age-related thymic involution, and these cells disappear following early thymectomy. Experiments in which variable numbers of the 14 thymic lobes are removed in young chicks indicate a direct correlation between the levels of circulating chT1+ cells and residual thymic mass. Measurement of recent thymic emigrants in the periphery thus provides an accurate indication of thymic function.

Characterization of a T cell lineage marker in carp (Cyprinus carpio L.)

A monoclonal antibody against thymocytes (WCL9; of IgG1 class) was produced by immunization of mice with isolated membrane molecules of carp thymocytes. Flow cytometric and fluorescence microscopic analysis showed that WCL9 was reactive with 30-50% of thymocytes and not with lymphoid cells from blood, pronephros, spleen and intestine. Cryo-sections of thymus showed a WCL9+ and WCL9- region in 3-month-old fish and only WCL9+ cells in 1-week-old fish. Because the WCL9- region is more medulla-like, the WCL9+ cells can be considered as cortical thymocytes. The majority of WCL9+ thymocytes appeared to have a higher density (1.06-1.07 g/mL) than the WCL9- cells (1.02-1.06 g/mL). Immunogold labelling or comparison of both density fractions did not show clear ultrastructural differences between WCL9+ and WCL9- thymocytes. The WCL9- fraction could be stimulated much better with PHA than the WCL9+ fraction. Removal of adherent cells or adding adherent accessory cells did not influence this result. Immunochemical analysis showed that WCL9 reacted with a protein determinant present on two molecules (M(r): 200 and 155 kDa) under reduced and non-reduced conditions. These results, together with the absence of WCL9+ cells in other lymphoid organs, strongly suggest that WCL9 is a specific marker for early thymocytes.

Thymocyte emigration in the chicken: an over-representation of CD4+ cells over CD8+ in the periphery

We have examined the emigration of chicken thymocytes after intrathymic fluorescein isothiocyanate (FITC) labelling in situ. In this paper we show that in young birds about 0.7% and 0.4% of thymocytes emigrate from the thymus to the blood and the spleen, respectively, per day. This suggests that, as in mammals, most thymocytes die within the thymus. At 3 weeks of age gamma delta and alpha beta T cells leave the thymus in comparable levels to their appearance in the blood. The phenotype of recent emigrants in peripheral tissues is similar to that of mature T cells. Interestingly, recent emigrants contain relatively much higher numbers of CD4+ and fewer CD8+ cells than is observed in peripheral tissues in a steady-state situation.

Identification of a T lineage antigen in the catfish

A murine monoclonal antibody produced against catfish thymocytes and immunoglobulin-negative lymphocytes in the blood identified a catfish T cell antigen designated CfT1. The CfT1 antigen was found to be expressed on thymocytes, a subpopulation of the lymphoid cells in blood and other lympho-hemopoietic tissues, and a T cell line, but was not expressed by erythrocytes, thrombocytes, myeloid cells, B cells or macrophage cell lines. Stimulation of blood mononuclear cells with the T cell mitogen, concanavalin A, resulted in an increased frequency of CfT1+ cells. Conversely, lipopolysaccharide stimulation increased the number of IgM+ B cells and decreased the frequency of CfT1+ cells. The CfT1 antigen was defined as a single chain protein of M(r) 35,000 lacking N- and O-linked sugars. The CfT1 molecule thus provides a T lineage-specific marker in this bony fish representative.

Selective mitomycin C and cyclophosphamide induction of apoptosis in differentiating B lymphocytes compared to T lymphocytes in vivo

Differentiating B and T lymphocytes differ in sensitivity to a number of environmental toxins and anticancer agents. B lymphocytes are susceptible and T lymphocytes resistant to killing by cyclophosphamide (Cy) metabolites capable of forming DNA interstrand cross-links. However, the mechanisms responsible for the rapid killing and loss of bursal-resident B lymphocytes are unknown. Therefore, we investigated the cellular mechanisms of selective toxicity of two cross-linking drugs, mitomycin C (MMC) and Cy, towards differentiating B and T lymphocyte populations using the chicken embryo model system. Viability of bursal-resident B lymphocytes (bursacytes) decreased starting at 5 h post exposure (PE) to MMC, and was maximally reduced by 71.6% by 10 h PE at the highest dose examined (9.0 micrograms MMC/g). Dose-dependent increases in the percentage of apoptotic bursacytes were observed as early as 5 h PE, and increased to 72% by 10 h PE. This was accompanied by reductions in bursacyte numbers. Cy also induced apoptosis in bursacytes. In contrast, thymus-resident lymphocytes (thymocytes) were much more resistant to the toxic effects of MMC and Cy. Viability of thymocytes was reduced by only 10% in the 9.0 micrograms/g MMC treatment group. In addition, the percentage of thymocytes engaged in apoptosis was much lower than that for bursacytes. MMC induced modest cell cycle inhibition in bursacytes and thymocytes. These data strongly suggest that MMC and Cy-induced diferential toxicity involves primarily early and extensive triggering of apoptosis in differentiating B lymphocytes, leading to rapid reduction of lymphocyte numbers in the embryonic bursa.

Membrane immunoglobulin-associated molecules on channel catfish B lymphocytes

Membrane immunoglobulin (mIgM) on the surface of channel catfish B lymphocytes is non-covalently associated with 64 and 70 kDa molecules which are composed of covalent 32 kDa dimers and covalent 45/25 kDa subunits, respectively. Cross-linking of mIgM on catfish B cells leads to rapid phosphorylation of tyrosine residues in these presumed accessory as well as numerous other cytoplasmic molecules. These data indicate that fish likely use a signal transduction system containing elements similar to those of mammalian B cells.

Participation of a chicken thymocyte antigen in intrathymic differentiation of T cells in vivo

The participation of CETHB1 antigen in the intrathymic development of T cells was analysed in sublethally X-ray irradiated chickens and normal embryos which were inoculated with anti-thymocyte monoclonal antibody CETHB1. When chickens were given a sublethal X-ray irradiation on the day of hatchings immature thymocytes existed prominently in the thymus up to 3 weeks after irradiation. The inoculation of CETHB1 monoclonal antibody on days 14 and 18 after irradiation caused an increase of CD4- CD8- cells and a decrease of CD4+ CD8+ cells as compared to changes in control chickens. However, expression of T cell receptors CD3, alphabetaTCR, and gammadeltaTCR was not influenced. Inoculation of the monoclonal antibody on embryonic days 13 to 16 resulted in a decrease of CD4+ CD8- cells and an increase of CD4-CD8- and CD4+ CD8+ cells after hatching. Thus, the binding of CETHB1 monoclonal antibody to thymocytes can inhibit the differentiation of both CD4-CD8- and CD4+ CD8+ cells to CD4+ CD8+ and CD4+ CD8- or CD4-CD8+ cells, respectively. These results suggest that CETHB1 antigen participated in the growth and differentiation of thymocytes in the thymic microenvironment.

Selective expression of major histocompatibility complex (MHC) antigens and modulation of T-cell differentiation in chickens with increased MHC-chromosome dosages

Increased dosage of genes belonging to the immunoglobulin superfamily may be responsible for some of the less noticeable but targeted phenotypic disturbances seen in trisomy conditions of humans and animals. We used an avian aneuploidy model to study the specific effects of extra major histocompatibility complex (MHC)-microchromosome dosage on the progression of thymocyte differentiation through a broad period of embryonic and neonatal development. The particular goal in the present investigation was to determine whether a reduction in the number of thymocytes, previously observed in the developing thymus of MHC aneuploids, is accompanied by particular alterations in thymocyte differentiation. We hypothesized that the subpopulation structure and/or developmental pattern for thymocyte differentiation are characteristically perturbed (delayed or modified) by increased MHC-chromosome dosage in cells. The regulation of MHC surface antigen expression in aneuploid thymocytes was also studied to detect dosage-dependent expression for one and possibly more sub-regions (class I, II, IV) of the avian MHC. Surface densities of MHC class I antigens on thymocytes were increased significantly at all ages studied, for example by 15% and 45% in trisomics and tetrasomics, respectively at 22 days post-hatching. The surface density of CT1 antigen, a thymocyte-specific marker, was also increased in a dosage-dependent manner, but only in juveniles. Increases in the proportion of alpha beta 1, TCR+ and CD3+ thymocytes were observed in juveniles, with no alterations in other TCR-expressing thymocytes. No major alterations in CD4 and CD8 thymocyte populations were observed. These results demonstrate a targeted effect of extra MHC-chromosome dosage towards enhanced class I and CT1, and not class II or IV, expression. The increased MHC-microchromosome dosage appears to influence primarily immature thymocytes expressing alpha beta 1 TCR and CD3.

Characterization of avian natural killer cells and their intracellular CD3 protein complex

Natural killer (NK) cell activity appears to be conserved throughout vertebrate development but NK cells have only been well characterized in mammals. Candidate NK cells have been identified in the chicken as cytoplasmic CD3+ and surface T cell receptor (TCR)/CD3- (TCRO) lymphocytes that often express CD8. The fact that the TCRO cells are abundant in the embryonic spleen before T cells enter this organ allowed us to cultivate the embryonic TCRO cells using growth factors derived from activated adult lymphocytes. These TCRO cells were cytotoxic for an NK target cell line. They expressed cell surface CD8, a putative interleukin-2 receptor, CD45 and a receptor for IgG, but did not express CD4, major histocompatibility complex class II or immunoglobulin. Biochemical analysis of the cytoplasmic CD3 antigen revealed two of the three CD3 gamma, delta and epsilon homologues, and RNA transcripts for the third. The CD3 monoclonal antibody also precipitated a 32-kDa dimer that may represent a heterodimer of different CD3 constituents. TCR alpha and beta gene transcripts were not detected in the TCRO cells. These results indicate that the avian TCRO cell is the mammalian NK cell homologue. The shared evolutionary features of T cells and NK cells in birds and mammals support the idea that they derive from a common progenitor.

Effect of dietary vitamin E and selenium deficiency on chicken splenocyte proliferation and cell surface marker expression

Beginning at hatching, chicks were fed a Basal diet, without vitamin E or selenium (Se) or the same diet supplemented with vitamin E (100 IU/kg) and Se (0.2 ppm). The effect of these treatments on the expression of cell surface markers (CT-1a, CD3, CD4, CD8, sIgs, and Ia) defining specific thymocyte and peripheral blood leukocyte (PBL) subpopulations were examined using flow cytometric analyses. In parallel studies the effect of the dietary deficiencies on splenocyte proliferative responses to ConA or PHA stimulation was examined. The mean expression of CD3 and CT-1a per cell was increased while CD8 and CD4 expression was decreased on thymocytes from chicks fed the Basal diet. The proportion of double negative (CD4-, CD8-) thymocytes and single positive CD8+ thymocytes was significantly decreased while single positive CD4+ and double positive (CD4+, CD8+) thymocytes were significantly increased by the dietary vitamin E and Se deficiencies. The dietary deficiencies resulted in a decreased proportion of peripheral T cells and specifically decreased the number of CD4+ PBL. The proliferative response to both ConA and PHA was impaired by the vitamin E and Se dietary deficiencies. The proliferative response could be fully reconstituted but only after vitamin E and Se supplementation for periods longer than 1 week. Plasma SeGSHpx and alpha-tocopherol levels paralleled the mitogen responsiveness observed. These results support the conclusion that vitamin E and Se deficiencies may affect both the maturation of specific lymphocyte subpopulations and the functional and proliferative capabilities of the peripheral lymphocytes.

Intra-embryonic haemopoietic cells and early MHC expression

In the avian embryo the haemopoietic stem cells originate from the intra-embryonic area near dorsal aorta. The surface-marker expression of haemopoietic stem cells and their potential to produce different haemopoietic cells are still largely unknown. The surface antigen expression and particularly the MHC antigen expression on intra-embryonic haemopoietic cells was studied. Expression of B-F antigens, homologous to mammalian MHC class-I antigens, was found already on embryonic day (ED) 5. The first B-L antigens, analogous to mammalian MHC class-II antigens, were detected also from ED5 onwards. The appearance of surface antigens defined by MoAbs T10A6 and 3-298 during embryogenesis also was studied. The antigen defined with T10A6 was detected from ED4 onwards on endothelial cells but not on haemopoietic cells in the para-aortic region. The first 3-298+ haemopoietic cells were found on ED6, whereas endothelial cells were negative. These findings imply that some surface markers are shared with haemopoietic and endothelial cells indicating either a common embryonic origin or the importance of these molecules in embryonic stem-cell homing.

Characterization of new monoclonal antibodies identifying avian T lymphocyte antigens

Six monoclonal antibodies (mAb) were produced to identify and characterize surface antigens of chicken T cells. Determination of their reactivity with different lymphatic cells using immunofluorescence analysis demonstrates that mAb KH8, NA6, PD4 and TH8 stained 32-43% blood lymphocytes, 72-77% thymocytes and 19-27% spleen cells, mAb OC5 approximately 99% thymocytes and 55% blood and spleen lymphocytes each, and mAb OC2 36% blood lymphocytes, 79% thymocytes and 62% spleen cells. The KH8, NA6, PD4 and TH8 antibodies immunoprecipitated from lysates of surface-labeled chicken thymocytes a polypeptide of M(r) 60,000 under non-reducing conditions and the OC5 antibody a glycoprotein of M(r) 68,000 under reducing conditions. MAb OC2 precipitated a single polypeptide of M(r) 40,000 under both conditions. The mAb KH8, NA6, PD4, TH8 and OC2 inhibited ConA-induced proliferative responses of blood T cells in vitro. However, sepharose-bound or soluble OC5 antibody was able to increase DNA synthesis significantly. These results indicate that (a) the mAb KH8, NA6, PD4 and TH8 identify the avian homologue of the mammalian CD4 molecule, (b) the mAb OC2 detects the avian CD2 antigen, and (c) the mAb OC5 recognizes the putative avian CD5 homologue.

Intestinal T lymphocytes in the chicken express an integrin-like antigen

We report the characterization of a molecule recognized on chicken T cells by the murine A19 monoclonal antibody that was generated by immunization with intestinal intraepithelial lymphocytes. Immunofluorescence analysis indicated that both alpha beta and gamma delta T cell subpopulations in the intestine express the A19 antigen, but natural killer cells and B cells do not. The A19-marked T cells were preferentially localized in the intestinal epithelium and less frequently in the underlying lamina propria. T cells appearing in the intestine during embryonic life were A19 negative but acquired the antigen within the first few days after hatching. Although rarely found on cells in non-intestinal tissues at any age, very late expression of the A19 antigen could be induced by concanavalin A stimulation of splenic and circulating T cells. Transforming growth factor beta 1 enhanced this induction of A19 expression. The A19 molecules expressed by intestinal T cells and activated splenic T cells were biochemically identical, consisting of a multi-molecular complex of proteins with approximate M(r) of 205, 145 and 75 kDa under nonreducing conditions and 120, 90 and 28 kDa under reducing conditions. The characteristics of this multimolecular complex and its differential expression suggest that the A19 antigen is a member of the integrin family which may function in the retention of intestinal lymphocytes.

The effect of synthetic thymulin on cell surface marker expression by avian T-cell precursors

The effects of the in vitro exposure of avian bone marrow (BM) cells and thymocytes to synthetic thymulin were studied. Two T-cell differentiation markers, PNA binding site and CT-1a expression, were used to examine cell maturation. Enhanced PNA binding to both BM cells and thymocytes resulted following an in vitro thymulin exposure but cell proliferation was not affected. Scatchard analysis supported the conclusion that PNA binding affinity was significantly increased and thus responsible for the observed increase in PNA binding. Flow cytometric analysis suggested that the induced PNA+ thymocyte population may be a different population from the one exhibiting enhanced CT-1a expression following thymulin exposure. Taken together, the observations suggest that cells can express their further differentiation states without undergoing proliferation following in vitro thymulin stimulation.

Transformation of T-lymphocyte subsets by Marek's disease herpesvirus

Marek's disease herpesvirus (MDV)-transformed lymphoblastoid tumor cell lines were characterized for the presence of the surface markers. Monoclonal antibodies were used for CD3 (T-cell receptor [TCR] complex), TCR1, TCR2, and TCR3, CD4, CD8, and Ia antigen by indirect fluorescence staining followed by microscopic examination or flow cytometry. The lymphoblastoid cell lines were obtained from tumors from chickens infected with MDV (n = 44) or from local lesions induced by inoculation of allogeneic, MDV-infected chick kidney cells (n = 56). Lymphocytes were harvested from these lesions between 4 and 16 days postinoculation and cultured in vitro to establish cell lines. All cell lines expressed Ia antigen and CD3 and/or TCR and thus are activated T cells. Most of the cell lines developed from tumors were CD4+ CD8-; only one cell line was negative for both markers. Sixteen percent of the cell lines were TCR3+, while the remainder were TCR2+. The cell lines developed from local lesions were much more heterogeneous: 45% were CD4- CD8+, 34% were CD4- CD8-, and only 21% were CD4+ CD8-. The number of TCR3+ cell lines was larger than expected for the CD4- CD8+ and CD4- CD8- cell lines, as judged from the presence of these cells in the blood. These results indicate that several subsets of T lymphocytes can be transformed by MDV, depending on the pathogenesis of infection. Activation of T cells as a consequence of the normal pathogenesis or by allogeneic stimulation seem to be a first important step in the process of transformation.

Immunologic abnormalities in pathogen-free cats experimentally infected with feline immunodeficiency virus

Blood mononuclear cells from 47 cats experimentally infected with feline immunodeficiency virus (FIV) were examined by using monoclonal antibodies directed against feline CD4 and CD8 homologs, a pan-T-cell antigen, and cell surface immunoglobulin. Significant inversion of the CD4+/CD8+ T-cell ratio was observed only in cats that were infected for 18 months or more. This inversion was associated with a decrease in the absolute numbers of CD4+ T cells and a concomitant increase in CD8+ cells. However, the total numbers of circulating T and B cells were not significantly reduced. Cats infected with FIV for 24 to 28 months also had significantly elevated levels of serum immunoglobulin G (IgG), but normal levels of IgA and IgM. The long-term decline in CD4+ T cells and hypergammaglobulinemia observed in FIV-infected cats resemble the abnormalities occurring in humans after human immunodeficiency virus infection.

Identification of a CD4 homologue in the cat

Monoclonal antibody, Fel 7, produced against cat T cells, was found to react with a single-chain glycoprotein of Mr 65,000 present on a majority of the thymocytes, 40% of lymph node cells, 15% of splenocytes and 25% of blood mononuclear cells. Using a previously reported antibody that recognizes the feline CD8 antigen, approximately 65% of cat thymocytes were shown to express both the Fel 7 and fCD8 antigens, while 14% and 6% expressed either the Fel 7 or the fCD8 determinant respectively. The Fel 7 and fCD8 antigens were expressed by mutually-exclusive subpopulations of peripheral T cells, and not by B cells, macrophages or other types of blood cells. Expression of the Fel 7 antigen was down-regulated and the molecule was phosphorylated when T cells were stimulated with phorbol ester, while the expression of the fCD8 antigen was unaffected by this treatment. The addition of soluble Fel 7 antibodies efficiently blocked Con A-induced proliferation of T cells in a dose-dependent manner. The data suggest that the mAb Fel 7 identifies a feline CD4 homologue, providing an important reagent for the study of normal and abnormal T cell development in cats.

Bu-2, a novel avian cell surface antigen on B cells and a population of non-lymphoid cells, is expressed homogeneously in germinal centers

A monoclonal antibody (mAb), Hy30, was generated against bursal cells. Under reducing conditions, it immunoprecipitates a cell surface antigen with an apparent molecular weight of 66 kD that is distinct from immunoglobulin and MHC class II. The antigen recognized by Hy30 is found on greater than 95% of all bursal cells, on a population of thymus resident cells, and on blood, spleen, and marrow mononuclear cells. Immunohistological analysis of tissue sections revealed that the majority of the staining by Hy30 occurs in the B cell areas of the spleen and thymus. Flow cytometric analysis demonstrated that the antigen recognized by Hy30 is found on both immunoglobulin positive (Ig+) and negative (Ig-) cells. Analysis of a chicken rendered B cell deficient by treatment with cyclophosphamide at hatch confirmed this observation. In these birds, the medullary dendritic cells of the bursa and Ig- cells of the "B-cell areas" of the spleen and thymus expressed the Hy30 Ag. Analysis of several avian tumor lines did not suggest an obvious lineage for these Hy30+ Ig- cells. However, analysis of germinal centers suggested that these cells may be tissue macrophages or dendritic cells. This is consistent with previously reported histology of these "B-cell areas". Flow cytometric analysis of the antigen recognized by Hy30 demonstrates that it is distinct from the Bu-1 B-cell surface antigen and we designate it as Bu-2.

Analysis of the first two waves of thymus homing stem cells and their T cell progeny in chick-quail chimeras

Chick-quail chimeras were used to study precursor/progeny relationships of hemopoietic stem cells (SC) that enter the embryonic thymus in waves to give rise sequentially to the TCR-1+, TCR-2+, and TCR-3+ lineages of T cells. The first wave of SC and their progeny were examined by grafting thymus from 9-d chick embryos (E9) into E3 quails. mAbs specific for chick T cell antigens were used to trace the development of T cells in the recipients. All three lineages of TCR-bearing cells were generated from the first wave of SC. The cortico-medullary transit time was several day shorter for the TCR-1 subpopulation than for the TCR-2 subpopulation, and the peripheral seeding of TCR-2 cells also occurred later in development. The duration of thymocyte production from the first wave of SC that entered the thymus was approximately 3 wk, during which gradual cortical to medullary replacement by second wave SC progeny occurred. When the latter was examined, after transplantation of E7 quail thymus into E3 chick embryos, a sequential generation pattern for the TCR-1 and TCR-2 cell progeny was not evident. Finally, recirculation of T cells to the thymus medulla was defined in this avian model.

Cytoplasmic CD3+ surface CD8+ lymphocytes develop as a thymus-independent lineage in chick-quail chimeras

We have analyzed the embryonic development of a population of lymphoid cells that express a CD3 antigenic determinant in the cytoplasm but not on the cell surface. Since these cells lack T cell receptor (TcR) molecules, we have provisionally named them TCRO cells. Their development, expansion and distribution was investigated following transplantation of splenic and bursal fragments from chicken embryos into quail embryos. Since quail cells are not recognized by our panel of monoclonal antibodies against chicken TcR1, TcR2, TcR3, CD3, CD4 and CD8 molecules, these antibodies provided reliable markers for donor chick lymphocytes in the tissues of the quail recipients. Transplanted spleen and bursa both generated CD3+ cells, the number of which increased as a function of age. Notably, approximately half of these CD3+ cells expressed surface CD8, but none acquired TcR1 (gamma/delta), TcR2 (alpha/beta) or TcR3 expression. Since TCRO cells normally appear first in the spleen of 8-day chick embryos (E8), their generation in E6 splenic transplants indicated an extrathymic origin. The TCRO cells of chick splenic origin migrated to the spleen, bursa and thymus of the quail recipients. In six of seven chimeras acquiring CT3+ cells in the recipient thymus, these cells were restricted to the medulla and displayed the typical TCRO phenotype: CD3+CD8+TcR1-TcR2-TcR3-. These intrathymic TCRO cells also lacked the CT1 thymocyte antigen. We conclude that the TCRO cells represent a thymus-independent lineage of lymphoid cells that can migrate into a receptive thymus by rarely, if ever, differentiate into conventional T cells.

Expression of v-rel induces mature B-cell lines that reflect the diversity of avian immunoglobulin heavy- and light-chain rearrangements

The infection of newly hatched chickens with reticuloendotheliosis virus strain T (REV-T) and a nonimmunosuppressive helper virus, chicken syncytial virus, induces rapidly metastatic B-cell lymphomas. In vivo analysis of these tumors with monoclonal antibodies detected the expression of the B-cell surface markers immunoglobulin M (IgM), CIa, Bu2, and CLA-1, but not IgG, Bu1, or a T-cell surface marker, CT-1. Cell lines derived from tumors exhibited the same pattern of staining, suggesting that expression of cell surface markers does not change during in vitro cell line development. All cell lines examined synthesized IgM in varying amounts. Northern (RNA blot) analysis confirmed abundant expression of v-rel mRNA, and Southern analysis revealed rearrangement of both heavy- and light-chain immunoglobulin loci. Analysis of the light-chain locus demonstrated that 20 of 22 lines contained a single rearranged allele. With respect to specific restriction enzyme sites within the V lambda 1 gene, the active allele in any given clone was either diversified or nondiversified. In contrast, examination of the heavy-chain loci within these lines demonstrated that 16 of the 22 had both alleles rearranged. Further diversification of the V lambda 1 locus did not occur after prolonged in vitro passage of the cell lines. We propose that v-rel expression arrests diversification of the light-chain locus in these lymphoid cells, allowing the production of stable, clonal B-cell populations. The development of these and similar cell lines will make it possible to identify specific stages of avian lymphoid ontogeny and to study the mechanism of rearrangement and diversification in the avian B lymphocyte.

RAV-1 insertional mutagenesis: disruption of the c-myb locus and development of avian B-cell lymphomas

Infection of young chickens with RAV-1, a subgroup A isolate of avian leukosis virus, results in the development of lymphoid leukosis, a B-cell lymphoma characterized by provirus insertion into the c-myc locus. We report here that when 12- to 13-day-old embryos rather than 1-day-old chickens were infected with RAV-1, a novel B-cell lymphoma developed in which proviral insertions had activated expression of the c-myb gene. These tumors expressed elevated levels of a 4.5-kilobase myb-containing mRNA transcript that contained c-myb sequences not found in v-myb. The c-myc locus in these tumors appeared normal. The biological properties of the activated myb lymphoma were distinct from those of lymphoid leukosis. Metastatic disease developed within 7 weeks of infection. Distinct intermediate pathogenic stages with preneoplastic and primary neoplastic lesions were not detected. Although bursal tissues appeared to be nonmalignant on gross examination, Southern analyses of bursal DNA revealed the presence of tumor with the same clonal origin as abdominal lymphoma masses. The dependence on embryonic infection for development of activated myb lymphoma suggests that the target cells in which c-myb is activated are found only in embryos and are distinct from those cells that give rise to lymphoid leukosis.

TCR3: a third T-cell receptor in the chicken

Avian homologues of mammalian gamma delta and alpha beta T-cell antigen receptors, TCR1 and TCR2, have been identified with monoclonal antibodies. These TCR isotypes are associated with the avian CD3 proteins on the T-cell surface. During chick development, T-cell subpopulations bearing CD3/TCR1 or CD3/TCR2 receptor complexes are generated sequentially in the thymus and seeded to the periphery in the same order. In this study, we used two-color immunofluorescence to identify the subsequent development of a third subpopulation of T cells, provisionally named TCR3. These CD3+ cells, which expressed neither TCR1 nor TCR2, were first detected in the blood 1 week after hatching and increased numerically as a function of age to account for approximately 15% of the circulating T-cell pool in adults. Most (greater than 80%) of the TCR3 cells expressed the CD4 accessory molecule. The relative incidence of the TCR3 subpopulation increased dramatically as a consequence of embryonic treatment with anti-TCR2 antibody and thymectomy after hatching. Two disulfide-linked polypeptides, of Mr 48,000 and 40,000, were associated with the CD3 complex on the TCR3 cells. Examination of the TCR protein backbones and peptide mapping of the TCR chains after partial proteolysis indicated that the TCR3 heterodimer differs from both TCR1 and TCR2. These results suggest the existence of a third class of T-cell receptors in birds.

Expression of v-rel induces mature B-cell lines that reflect the diversity of avian immunoglobulin heavy- and light-chain rearrangements

The infection of newly hatched chickens with reticuloendotheliosis virus strain T (REV-T) and a nonimmunosuppressive helper virus, chicken syncytial virus, induces rapidly metastatic B-cell lymphomas. In vivo analysis of these tumors with monoclonal antibodies detected the expression of the B-cell surface markers immunoglobulin M (IgM), CIa, Bu2, and CLA-1, but not IgG, Bu1, or a T-cell surface marker, CT-1. Cell lines derived from tumors exhibited the same pattern of staining, suggesting that expression of cell surface markers does not change during in vitro cell line development. All cell lines examined synthesized IgM in varying amounts. Northern (RNA blot) analysis confirmed abundant expression of v-rel mRNA, and Southern analysis revealed rearrangement of both heavy- and light-chain immunoglobulin loci. Analysis of the light-chain locus demonstrated that 20 of 22 lines contained a single rearranged allele. With respect to specific restriction enzyme sites within the V lambda 1 gene, the active allele in any given clone was either diversified or nondiversified. In contrast, examination of the heavy-chain loci within these lines demonstrated that 16 of the 22 had both alleles rearranged. Further diversification of the V lambda 1 locus did not occur after prolonged in vitro passage of the cell lines. We propose that v-rel expression arrests diversification of the light-chain locus in these lymphoid cells, allowing the production of stable, clonal B-cell populations. The development of these and similar cell lines will make it possible to identify specific stages of avian lymphoid ontogeny and to study the mechanism of rearrangement and diversification in the avian B lymphocyte.

Differential expression of two T cell receptors, TcR1 and TcR2, on chicken lymphocytes

A monoclonal antibody, TcR2, has been shown to recognize an avian homologue of the mammalian alpha/beta T cell receptor (TcR). The TcR2-reactive molecule was found to be a T3-associated heterodimer with relative molecular mass of 90-kDa consisting of disulfide-linked 50-kDa and 40-kDa polypeptides. The sizes of the deglycosylated TcR2 polypeptides differed from those of TcR1, an avian homologue of the mammalian gamma/delta T cell receptor. Immunofluorescence analysis revealed that TcR1 and TcR2 are expressed on separate populations of T cells during their development first in the thymus and then in the periphery. Ontogenetic studies revealed that the TcR1+ thymocytes are generated first and the generation of TcR2+ cells begins approximately 3 days later. While most TcR2+ cells in the thymus expressed both CT4 and CT8, TcR2+ cells in blood and the spleen were either CT4+ or CT8+. The TcR1+ cells in blood and thymus were CT4-CT8-, but the majority of TcR1+ cells in the spleen surprisingly expressed the CT8 marker. The data suggest that TcR1 and TcR2 cells are generated in the thymus as separate T cell sublineages.

A large subpopulation of avian T cells express a homologue of the mammalian T gamma/delta receptor

This report describes an avian TCR molecule, TCR1, whose molecular characteristics, signal-transducing property, and tissue distribution suggest that it is a homologue of the mammalian TCR-gamma/delta. TCR1+ cells are the first to be generated in the thymus during ontogeny, preceding other T3+ cells by approximately 3 d. Unlike their mammalian counterpart, TCR1+ cells constitute a relatively large subpopulation of peripheral T cells in mature chickens. These results suggest a phylogenetically important role for this receptor in T cell development and function.

Monoclonal antibodies against chicken Bu-1a and Bu-1b alloantigens

The production and characterization of monoclonal antibodies (mAbs) against chicken B cell surface alloantigens, Bu-1a and Bu-1b, is described. Flow cytometric analysis using these mAbs demonstrates that Bu-1 gene locus does not show allelic exclusion. Two color fluorescence analysis using simultaneous surface marker labeling and DNA staining shows that the expression of Bu-1 antigen is not restricted to a specific phase of the cell cycle. Earlier findings that Bu-1 locus is not linked to the MHC locus are confirmed. Furthermore, data is presented that Bu-1 antigen expression is not entirely B cell restricted. Apparently a fraction of larger mononuclear cells with typical light scatter characteristics in flow cytometry also bear this marker. MAbs against both allelic Bu-1 antigens are beneficial tools e.g. in typing of chicken lines and in studies on chicken B cell differentiation.

The effect of alterations in myc gene expression on B cell development in the bursa of Fabricius

Infection of 18-day embryonic bursal lymphocytes with a v-myc-containing retrovirus leads directly to a polyclonal proliferation of surface immunoglobulin-positive (slg+) cells in the bursa of Fabricius detected four weeks after hatching. These v-myc-expressing bursal cells repopulate the follicles of chemically ablated bursae more efficiently than total normal 18-day embryonic bursal cells. In contrast, comparable normal bursal cells lose the ability to repopulate follicles by four weeks. Bursal lymphocytes expressing either a retroviral v-myc or a c-myc gene deregulated by adjacent retroviral integration retain the ability of embryonic bursal lymphocytes to diversify their immunoglobulin light chain genes. These results suggest that retroviral deregulation of myc expression during avian B cell development induces outgrowth of a population of cells with the cardinal phenotypic characteristics of bursal stem cells.

Monoclonal antibody identification of a type II alveolar epithelial cell antigen and expression of the antigen during lung development

A monoclonal antibody identifying an antigen expressed by rat type II alveolar epithelial cells, but not by type I epithelial cells or other mature lung cells, was produced by immunization of mice with cells of the rat L2 cell line. The antigen recognized by the antibody was present on the microvillous luminal surface of type II epithelial cells. In adult rat lung, only type II epithelial cells bound the antibody. During fetal development the antigen was expressed by cuboidal epithelial cells lining the respiratory ducts of the first divisions of the tracheal bud, but not by epithelial cells lining the esophagus or trachea. The antigen continued to be expressed by cuboidal epithelial cells lining the larger respiratory ducts until approximately 19 days gestational age. Thereafter, expression was increasingly limited to selected single cells or clusters of two to four cuboidal cells in the smallest ducts. By the 21st postnatal day, the antigen was expressed only by type II alveolar epithelial cells. Type II alveolar epithelial cells isolated from adult lung and the L2 cell line in culture expressed the antigen on the cell surface. A protein of approximately 146,000 Mr was isolated by immunoadsorption of the antigen from non-ionic detergent extracts of type II cells and L2 cells. Preliminary studies of the binding of the antibody to other rat tissues indicate that the antibody binds to renal proximal tubular epithelial cells of the kidney and the luminal surface of the small bowel epithelial cells.

Relationship between immune system and gram-negative bacteria, binding of Salmonella pullorum-gallinarum to chicken lymphocytes

Salmonella pullorum-gallinarum binding to chicken lymphocytes has been evaluated in individuals of different age (1-20 wks). Bacterial adherence has been studied on lymphoid cells recovered from thymus, spleen, bursa and peripheral blood. Binding was age-dependent and neuraminidase treatment of lymphoid cells led to an increase of adherence. In addition, by using two monoclonal antibodies, the CT-1, which defines thymocytes and the M-4 which identifies surface IgM and an avian homologue of mammalian IgD on B lymphocytes, distribution of Salmonella pullorum-gallinarum binding to T and B lymphocytes has been analyzed. Results show that either T lymphocytes or B lymphocytes have the capacity to form rosettes with Salmonella. In particular, B cells from bursa and spleen display the highest capacity of adherence to bacteria, this supporting the defence function which has been attributed to bursa of Fabricius.

Analysis of a surface protein of Streptococcus pneumoniae recognised by protective monoclonal antibodies

Using two monoclonal antibodies which protect mice from a fatal challenge with S. pneumoniae, we have identified a surface protein antigen on the pneumococcus. These antibodies recognised components of 84 and 76 kD in a cell wall extract of the nonencapsulated strain, R36A, against which they were made. Absorption experiments indicated that both of the antibodies recognised the same two proteins. The proteins detected by the antibodies in the encapsulated type 2 strain D39 and type 3 strain WU2, exhibited different molecular weights than those proteins detected from R36A. Using a colony blot procedure and a quantitative ELISA, we have shown that these antibodies react with 6 of the 21 pneumococcal strains tested. There was no association between reactivity with these anti-protein antibodies and the capsular serotype of the pneumococcal isolates tested.

Selective integration of avian leukosis virus in different hematopoietic tissues

Hematopoietic tissues obtained from avian leukosis virus (ALV)-infected Hyline SC chickens were analyzed for the presence of integrated viral DNA sequences. Cells were prepared from bone marrow, bursa, spleen, thymus, and peripheral blood. Following the removal of erythrocytes, cellular DNAs from each of these tissues were examined by Southern analysis. During the first few weeks of infection, DNA from the bone marrow contained as many as 0.5 copies of viral DNA per haploid genome. Cells from the bursa and peripheral blood contained between 0.05 and 0.15 copies per haploid genome. In contrast, neither splenic nor thymic DNA contained significant levels of viral DNA sequences even though infected birds developed titers of circulating virus between 10(5) and 10(6) IU/ml of plasma. DNA prepared from erythrocytes isolated from the peripheral blood of these birds contained approximately 0.4 copies of integrated viral sequences per haploid genome at 2 weeks after infection. Despite greater levels of integrated sequences in other tissues, by 9 weeks after infection viral sequences were detected only in DNA from bursal lymphocytes. Cells prepared from the spleen and thymus of infected birds were also examined for their size distribution, their internal complexity and their surface expression of immunoglobulin. None of the populations examined differed from normal, uninfected control preparations. These results suggest that ALV infection occurs primarily in the bone marrow and that the different tissues of the hematopoietic system are selectively infected. Further, these results indicate that ALV infection persists longer in bursal lymphocytes than in other hematopoietic tissues. Previous studies have demonstrated that the lymphoid tumors that develop in white leghorn chickens following ALV infection are bursal-dependent B-cell lymphomas that express immunoglobulin M. The observations presented in this communication offer, in part, an explanation for the restricted phenotype of the lymphoid tumor that develops in the SC chicken. Further, the data suggest an explanation for the bursal-dependent nature of the ALV-induced lymphoma.